Switching element for a valve drive of an internal combustion engine

ABSTRACT

A switching element ( 1 ) for a valve drive of an internal combustion engine, preferably for shutting off valves, is provided, and includes an external part ( 2 ) in whose bore ( 3 ) an inner element ( 5 ) is axially movable. The external part ( 2 ) and the inner element ( 5 ) have at least a respective mutually aligned recess ( 7, 8 ) due to an axially spaced relative position obtained through a lost motion spring ( 6 ), and in one of the recesses, in the direction of the other recess, displaceable coupling means ( 9 ) are mutually applied in the relative position for coupling the inner element ( 5 ) with the external part ( 2 ). Two pistons ( 10 ) are provided as coupling means ( 9 ), which travel in the recess ( 8 ) formed as a radial bore of the inner element ( 5 ), and which diametrically oppose one another. The recess ( 7 ) of the external part ( 2 ) is formed as an annular groove ( 16 ) in the bore ( 3 ), and the pistons ( 10 ) at their underside ( 17 ) remote from the cam, starting from their radially external end faces ( 13 ), sectionally have a planar transverse surface ( 14 ) as contact region to a facing annular surface ( 15 ) of the annular groove ( 16 ), and the pistons ( 10 ) are guided with rotation securement ( 19 ) in the inner element ( 5 ). This provides a switching element ( 1 ) which has a simply constructed coupling mechanism, which produces only a small component loading.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/EP02/14431, filed Dec. 18,2002, which is incorporated herein by reference as if fully set forth.

BACKGROUND

The invention relates to a switching element for a valve drive of aninternal combustion engine, preferably for shutting off valves, with anexternal part in whose bore an inner element is axially movable, theexternal part and the inner element having at least one respectivemutually aligned recess due to an axially spaced relative positionobtained by a lost motion spring, and in one of the recesses, facing inthe direction of the other recess, displaceable coupling means aremutually applied in the relative position for coupling the inner elementwith the external part.

Such a switching element, constructed here as a cam follower in a tappetpush rod gear, is known from DE 199 15 531. It is disadvantageous inthis that only one piston is provided as the coupling means. It is clearto one skilled in the art that there is a high component loading in thecoupling region because of the single piston coupling. There is also arelatively great danger of tilting of the inner element with respect tothe external part. It is disadvantageous that a bore is provided as therecess into which the piston travels as coupling means. An extremelyundesired edge loading can occur here when the coupling means travelsout insufficiently, because of the special penetration of the bodies.

SUMMARY

The object of the invention is therefore to provide a switching elementof the kind mentioned at the beginning, in which the cited disadvantagesare eliminated with simple means.

This object is attained according to the invention in that two pistonsare provided as coupling means, which travel in the recess formed as aradial bore of the inner element, and which diametrically oppose oneanother there, the recess of the external part being formed there as anannular groove in the bore, and the piston at its underside remote fromthe cam, starting from its radially external end face, sectionally has aplanar transverse surface as contact region to a facing annular surfaceof the annular groove, and the piston being guided in a rotationallysecure manner in the inner element.

A switching element with a very secure coupling mechanism is herebyprovided. The component loading, and likewise the tilting movement, aregreatly reduced by the two-piston locking. On the other hand it is to beobserved that a coupling aperture which is easy to make is present inthe external part because of the recess in the external part beingformed as a peripheral annular groove. According to the invention, thepistons have on their underside a planar surface as contact region forthe annular groove, so that the surface pressure is greatly reducedhere. In other words, through the measures according to the invention,the cam stroke is transferred to the inner part over very large bearingsurfaces. If necessary, more than two coupling means can be arranged inthe inner element; preferably these are then symmetrically distributed.

So that the planar transverse surface is always in contact with theannular surface of the annular groove, the pistons are fixed againstrotation in their recess by means of a simple rotational securement.Here, in one specific embodiment of the invention, for example, asurrounding snap ring is present enclosing the inner element and onwhich the cross section of the piston abuts in the recess region. Thepistons can of course be themselves secured against rotation in theirrecess by means of flats or spring-groove embodiments.

As a further development of the invention, it is proposed to provide astop for the piston in the inner element. This is arranged centrally, sothat both pistons always have the same travel path radially outward.

Preferably the radial bore in the inner element is made as a throughbore. An offset or stepped construction is however also conceivable, sothat the said spring ring or a similar means can be dispensed with.

It is particularly advantageous if the radially outward end face of thepiston, at least in the edge region toward the transverse surface, has acurvature correlating with the bore of the inner element. It is thusclear that a good bearing region is already provided with even thesmallest travel of the piston into the annular groove of the externalpart.

A further particularly preferred embodiment of the invention relates tothe end side of the piston connecting the transverse surface with theunderside having a curvature correlating to the bore of the innerelement, or being beveled like a roof. It is thus clear that by means ofthese simple measures the pistons can travel out radially very far inthe annular groove in the case of coupling, and thus form an outstandingsupport pattern.

The scope of this invention relates expressly to all kinds of switchingelements in valve drives such as cam followers in tappet push roddrives, support elements for finger levers, bucket tappets, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is appropriately described with reference to the drawings.

FIG. 1 is a longitudinal section through a switching element constructedas a roller tappet according to the invention,

FIG. 2 is a partial longitudinal section, turned through 90° accordingto FIG. 1,

FIG. 3 is a partial longitudinal section similar to FIG. 2,

FIG. 4 is a bottom view of a piston as coupling means,

FIG. 5 is a cross-sectional view of the piston, and

FIGS. 6 and 7 show alternative embodiments to FIGS. 4 and 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1-3 disclose a switching element 1 for a valve drive of aninternal combustion engine. This is constructed here as a roller tappetfor a tappet push rod drive. It includes an external part 2, in whosebore 3 the external surface 4 of an axially movable inner element 5runs. The external part 2 and the inner element 5 are urged apart by alost motion spring 6, not further described.

In the axially separated position of the external part 2 from the innerelement 5 as described in the drawing, the recesses 7, 8 are mutuallyaligned. The recess 7 of the external part 2 is made as a peripheralannular groove 2. The recess 8 in the inner element 5, on the contrary,is made as a through bore extending radially. A path like a bowstringchord, or skew, is likewise conceivable.

Two diametrically opposed coupling means 9 are arranged in the recess 8of the inner element 5. These are formed as pistons 10 here, and areurged apart by a compression spring means 11. A stop for the pistons 10is provided centrally in the recess 8. This is provided as an annularpart such as a snap ring. Thus in a decoupling position of the pistons10, their central position and thus equal travel path is guaranteed.

As shown in detail in FIGS. 4-7, the pistons 10 sectionally have aplanar transverse surface 14 starting from their radially outer end face13. This acts as contact region to a facing annular surface 15 (seeFIGS. 1-3) of the recess 7 formed as an annular groove. As can be seen,the coupling aperture in the external part 2 is formedcircumferentially; this has manufacturing advantages, for example.

The end face 13 of the piston 10 can be curved, as shown in FIG. 4, ascan the bore 3 of the external part 2. Thus a good bearing pattern isimmediately set up when the piston 10 travels into the annular groove16. So-called edge supports are effectively avoided.

As can be seen from FIGS. 4 and 6, an end side 18 of the piston 10connecting the transverse surface 14 with an underside 17 remote fromthe cam is likewise provided with a curvature correlating with the bore3 of the external part 2 or, as shown in FIG. 6, is beveled like a roof.

Since the transverse surfaces 14 of the pistons 10 have to be alwaysfacing the annular surface 15 of the annular groove 16 in the externalpart 2, a simple rotational securement 19 is provided for the pistons 10(see FIG. 2). This comprises an annular part such as a snap ring, whichis arranged in an annular groove 20 on the external surface 4 of theinner element 5. The rotational securement 19 runs at such a height asto engage under the transverse surface 14 of the pistons 10.

FIG. 3 shows an alternative measure to the central stop 12 for thepistons 10. This is provided here as a component 21 such as a pin,projecting orthogonally into the recess 8, formed as a radial bore, ofthe inner element 5.

Thus a switching element is present which has a very secure and simplybuilt coupling mechanism which produces only a very small componentloading.

List of Reference Numerals

-   1 switching element-   2 external part-   3 bore-   4 external surface-   5 inner element-   6 lost motion spring-   7 recess-   8 recess-   9 coupling means-   10 piston-   11 compression spring means-   12 stop-   13 end surface-   14 transverse surface-   15 annular surface-   16 annular groove-   17 underside-   18 end side-   19 rotation securement-   20 annular portion-   21 pin component-   22 edge region

1. Switching element (1) for a valve drive of an internal combustionengine for shutting off valves, comprising an external part (2) with abore (3) in which an inner element (5) is axially movable, the externalpart (2) and the inner element (5) having at least a respective mutuallyaligned recess (7, 8) due to an axially spaced relative positionobtained by a lost motion spring (6) acting between the inner elementand the external part, and in one of the recesses, in a direction of theother recess, a displaceable coupling mechanism (9) is provided forcoupling the inner element (5) with the external part (2), wherein twopistons (10) are provided as the coupling mechanism (9), which travel inthe recess (8) formed as a radial bore of the inner element (5), andwhich diametrically oppose one another, the recess (7) of the externalpart (2) being formed as an annular groove (16) in the bore (3), and thepistons (10) have an underside (17) and starting from a radially outerend face (13) of the pistons, sectionally have a planar transversesurface (14) as a contact region to a facing annular surface (15) of theannular groove (16), and the pistons (10) are guided by a rotationsecurement (19) in the inner element (5).
 2. Switching element accordingto claim 1, wherein the rotation securement (19) comprises an annularpart which extends in an annular groove (20) on an external surface (4)of the inner element (5) and is arranged at a height such that theannular part engages under the planar transverse surface (14) of thepiston (10).
 3. Switching element according to claim 1, wherein therecess (8) in the inner element (5) has a stop (12) for radially innerend faces of the pistons (10), and the stop (12) is positionedcentrally.
 4. Switching element according to claim 3, wherein the recess(8) is formed as a through bore, and the stop (12) is formed as one ofan annular part located in the through bore, or a component (21) thatprojects orthogonally into the through bore.
 5. Switching elementaccording to claim 1, wherein the radially outer end face (13) of thepiston (10), at least in an edge region (22) to the transverse surface(14), has a curvature corresponding to the bore (3) of the inner element(5).
 6. Switching element according to claim 1, wherein an end side (18)of the piston (10), connecting the transverse surface (14) with theunderside (17), has a curvature correlating to the bore (3) of the innerelement (5), or is formed with a roof-like bevel in a bottom surfacethereof.
 7. Switching element according to claim 1, wherein theswitching element (1) is produced as a cam follower in a tappet push roddrive.
 8. Switching element according to claim 2, wherein the recess (8)in the inner element (5) has a stop (12) for radially inner end faces ofthe pistons (10), and the stop (12) is positioned centrally.